DO WE WANT to control illegal immigration, now running at an estimated rate of several million a year? Until recently the broad answer was no. The Immigration Service and law-enforcement groups were ready, but two other actors in this then-subdued social drama, employers seeking cheap labor and His-panic-Americans welcoming kin, were not. Only when unemployment among American citizens rose (it's now at eight million) and aliens spread in considerable numbers beyond the Southwest did the problem come to seem important and national. The Ford administration responded by commissioning the government's first comprehensive study, a first-rate report completed last December. Taking up where Mr. Ford left off, Mr. Carter is trying to compose a workable and reasonably coherent policy now.

A country can't let its immigration laws be flouted. It's unnatural that a full 10 per cent of the population of Mexico may be in the United States illegally.In theory, we could replace the open 2,000-mile Mexican frontier with a Berlin Wall and impose Soviet-style controls on incoming "tourists" and "students." But few Americans would wish to pay that sort of society-transforming price. So all the remedies reportedly being considered by the administration are palliatives. One is tighter border policing. Another is to issue legal aliens "non-forgeable" identity cards and then demand, in legislation, that employers not hire illegals. Like earlier students of the issue, President Carter has already decided to grant "amnesty" to some illegals. Amnesty rewards lawbreaking, but rooting out all the illegals would be, on the one hand, impossible and, on the other, socially and personally disruptive in the extreme.

The consensus supporting concerted government action is growing, but it's hindered by poor information. For instance, those favoring amnesty for illegals who have been here, say, five years don't know whether that step would make three or 13 million new citizens. The effects on the service burdens of state and local governments are only guesses. The Carter planners figure it makes sense to attack the problem at its source by encouraging job creation in Mexico and elsewhere but, aside from the hot argument over whether the United States should create foreign jobs in the first place, no one knows what specific benefits that strategy would bring. Only recently have diplomats even begun to ask what the foreign-policy effects of controlling illegal immigration would be.

Given the "newness" of the problem, there is a strong argument for the problem, there is a strong argument for administration to take a non-doctrinaire approach and to regard the submission of legislation as, in the first instance, a discovery proceeding. Mr. Carter is said to be a month away from moving. He needn't think he has to come up with hard and fast answers. He might do better to join the national inquiry.